Dynamic SOC Range Adjustment for Hybrid Excavator Engine Start
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Solution Overview
Problem
Conventional hybrid-type hydraulic excavators face issues with engine start performance due to insufficient power in the electricity storage device, leading to potential engine stalling, increased fuel consumption, and excessive exhaust emissions, especially when the state of charge (SOC) falls below a certain threshold.
Innovation Solution
A construction machine equipped with an engine, electric motor, hydraulic pump, electricity storage device, and a main controller that adjusts the charge/discharge range of the electricity storage device by lowering the lower limit value to ensure sufficient power for engine start, while preventing over-discharge or over-charge, and provides engine stop prohibition information to operators when power is insufficient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electricity storage device is controlled to maintain SOC at an intermediate point (50-60%) to prevent over-discharge or over-charge, then the degradation prevention and effective use of power is improved, but the power availability for engine start is reduced
Solution Approach 1:
The patent applies dynamics by making the charge/discharge control range adjustable rather than fixed. The control unit dynamically changes the SOC range based on engine operation state: maintaining 50-60% during normal operation for degradation prevention, but allowing discharge down to 20% or lower during engine start conditions to ensure sufficient power availability. This dynamic adjustment resolves the contradiction between reliability and power availability.
Solution Approach 2:
The patent changes the parameter of SOC control range based on operating conditions. During normal operation, the SOC is maintained at 50-60% to prevent degradation. During engine start conditions, the control unit allows the SOC to drop to 20% or lower to provide sufficient discharge power. This parameter change strategy resolves the contradiction by adapting the control range to different operational requirements.
2Power
If the engine continues to operate to charge the electricity storage device when SOC falls below the lower limit value, then the power necessary for the next engine start is secured, but the fuel consumption increases and exhaust emissions increase
Solution Approach 1:
The patent applies preliminary action by proactively lowering the lower limit value of the charge/discharge range before the engine start condition occurs. When the control unit detects an engine start command, it immediately expands the discharge range to 20% or lower, ensuring sufficient power is available without requiring the engine to continue running for charging. This preliminary preparation eliminates the need for post-start charging operations.
Solution Approach 2:
The patent allows partial discharge beyond the normal lower limit (50-60% SOC) by permitting discharge down to 20% or lower during engine start conditions. This excessive discharge action provides sufficient power for engine start without requiring the engine to continue operating for charging, thus avoiding the energy loss and emissions that would result from extended engine operation.
3Reliability
If the lower limit value of the charge/discharge range is maintained to prevent over-discharge, then the degradation prevention is improved, but the engine start performance is reduced
Solution Approach 1:
The patent makes the lower limit value dynamic rather than fixed. During normal operation, the lower limit is maintained at 50-60% to prevent degradation. During engine start conditions, the control unit dynamically lowers the limit to 20% or lower to ensure sufficient discharge power for engine start. This dynamic adjustment resolves the contradiction between degradation prevention and engine start performance.
Solution Approach 2:
The patent changes the lower limit parameter of the charge/discharge range based on engine operation state. The control unit maintains the lower limit at 50-60% during normal operation but lowers it to 20% or lower when engine start is commanded. This parameter change ensures both degradation prevention during normal operation and sufficient power availability during engine start.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances engine start performance by ensuring power availability, reduces the risk of inadvertent engine shutdown, and allows for immediate engine stop without unnecessary charging, thereby minimizing fuel consumption and emissions.
Implementation Method 1
an electric motor connected mechanically to the engine... an electric motor function of assisting in the engine by power running using power of the electricity storage device
Implementation Method 2
The motor generator has an electric generator function of charging the electricity storage device with power generated by a driving force of the engine
Data Source
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AI summary
At the time of starting up an engine (9) using an assist motor generator (10), a main controller (28) lowers a lower limit value in a charge/discharge range of an electricity storage device (19) from a first lower limit value (min1) to a second lower limit value (min2) through an energy management control part (28B). The main controller (28) heightens the lower limit value in the charge/discharge range of an electricity storage device (19) from the second lower limit value (min2) to the first lower limit value (min1) when the start of the engine (9) is completed. Further, the main controller (28) displays engine stop prohibition information on a display device (30) when the start of the engine (9) is completed and when an SOC of the electricity storage device (19) falls below the first lower limit value (min1).